1. Field of the Invention
The present invention relates to optical films, polarizing plates, liquid crystal panels, and image display apparatuses.
2. Description of the Related Art
An anti-reflection or antiglare film for suppressing glare from extraneous light is generally disposed on an image display surface in an image display apparatus such as a liquid crystal display (LCD), a cathode ray tube display (CRT), a plasma display (PDP), an electroluminescence display (ELD), or a field emission display (FED).
An antireflection film mainly includes a light transmissive substrate; a hard coat layer disposed on the light transmissive substrate; and a low refractive index layer disposed on the hard coat layer. The antireflection film reduces reflected light in itself by countering light reflected on a surface of the low refractive index layer and light reflected an interface between the low refractive index layer and the hard coat layer with each other.
However, such an antireflection film has a problem that a rainbow-colored uneven pattern called an interference fringe is generated by interference of light reflected on an interface between a light transmissive substrate and a hard coat layer and light reflected on an interface between a low refractive index layer and the hard coat layer due to a difference between the refractive indices of the light transmissive substrate and the hard coat layer.
Against such a problem, there has been developed a technology, in which, when a hard coat layer is formed on a light transmissive substrate, the upper part of the light transmissive substrate is permeated by the constituent of a composition for a hard coat layer, a mixture region, in which the constituent of the light transmissive substrate and the constituent of the hard coat layer are mixed, is formed in the vicinity of an interface between the light transmissive substrate and the hard coat layer, and a difference between the refractive indices of the light transmissive substrate and the hard coat layer is reduced by the mixture region to allow prevention of generation of interference fringes (e.g., see Japanese Patent Laid-Open No, 2003-131007).
However, since the surface of the hard coat layer is flat in the antireflection film, the prevention of the generation of the interference fringes requires the formation of the mixture region having a sufficient thickness. Further, when the mixture region having a sufficient thickness is formed, desired hardness may not be obtained in the antireflection film if the thickness of the hard coat layer on the mixture region is not increased, since the mixture region is comparatively soft. Thus, there is a problem that it is necessary to thickly apply the composition for a hard coat layer on the light transmissive substrate, so that a manufacture cost becomes high.
On the other hand, an antiglare film includes a light transmissive substrate; and an antiglare hard coat layer that is disposed on the light transmissive substrate and has concavities and convexities on a surface thereof (e.g., see Japanese Patent Laid-Open No. 2011-81118). According to the antiglare film, extraneous light can be diffusely reflected by the concavities and convexities on the surface of the antiglare hard coat layer.
In the antiglare film, since interference fringes can be made to be invisible by the concavities and convexities on the surface of the antiglare hard coat layer, the thickness of a mixture region or the antiglare hard coat layer can be made to be smaller than that of the mixture region or hard coat layer of the antireflection film.
Currently, the need for an optical film having surface glossiness, such as the antireflection film, has been increased. However, the antireflection film has the problem that the manufacture cost thereof is high as described above. Further, the antiglare film has cloudiness since such concavities and convexities that antiglare properties are obtained are formed on the surface thereof. Therefore, surface glossiness is not obtained, so that the antiglare film has not been currently a substitute for the antireflection film.
The present invention was accomplished to solve the above-described problems. That is, the present invention is aimed at providing an optical film, a polarizing plate, a liquid crystal panel, and an image display apparatus, wherein interference fringes can be made to be invisible, cloudiness can be reduced, and a manufacture cost can be reduced.